In membrane transport and cell physiology, which of the following processes can occur without any direct expenditure of energy by the cell?

Introduction / Context:
This question examines your understanding of passive and active transport processes across cell membranes. Cells often move substances without spending metabolic energy, and such processes are termed passive. Knowing that diffusion and osmosis occur down a concentration gradient without direct ATP consumption is fundamental in physiology and biology examinations. The question asks you to identify which listed processes require no energy expenditure by the cell.

Given Data / Assumptions:
- The options list osmosis, diffusion, both together, and none. - Standard definitions of diffusion and osmosis as passive processes are assumed. - The phrase no energy from the cell refers to no direct use of ATP or other metabolic energy sources.

Concept / Approach:
Diffusion is the spontaneous movement of particles from a region of higher concentration to a region of lower concentration due to random thermal motion. Osmosis is a special case of diffusion where water moves across a semipermeable membrane from a region of higher water potential to a region of lower water potential. Both processes are passive and do not require ATP. By contrast, active transport pumps move substances against concentration gradients and always need cellular energy. Since both diffusion and osmosis are passive, the combined option correctly answers the question.

Step-by-Step Solution:
Step 1: Recall that diffusion is a passive transport mechanism where solute molecules move down their concentration gradient. Step 2: Recall that osmosis involves movement of water across a semipermeable membrane and is also driven by concentration differences rather than ATP usage. Step 3: Note that in both cases, movement is due to inherent kinetic energy of molecules and does not require metabolic energy from the cell. Step 4: Compare option A, which selects only osmosis, and option B, which selects only diffusion, and recognise that each alone is incomplete because both processes are passive. Step 5: Option C states both osmosis and diffusion, which correctly groups the passive processes that fit the requirement. Step 6: Conclude that both osmosis and diffusion require no direct energy from the cell and therefore option C is correct.

Verification / Alternative check:
As an alternative verification, consider examples. Oxygen entering cells from blood diffuses down its concentration gradient without ATP use, and water entering plant roots by osmosis also occurs passively. Textbooks classify both under passive transport, clearly differentiating them from sodium potassium pumps and proton pumps that require ATP. Checking this classification confirms that both processes meet the condition of requiring no energy from the cell.

Why Other Options Are Wrong:
Osmosis: This option alone is incomplete because diffusion is also a passive process that requires no energy from the cell. Diffusion: Choosing only diffusion ignores osmosis, which is similarly a passive movement of water and also fits the requirement. None of the above: This is incorrect because both osmosis and diffusion are classical examples of passive processes that occur without direct ATP expenditure.

Common Pitfalls:
Many learners think any movement of substances across membranes must use energy, leading them to wrongly rule out passive transport. Another pitfall is confusion between facilitated diffusion, which may involve proteins but still does not consume ATP, and active transport, which does. It is important to remember that the key difference is whether substances move down or against a concentration gradient. If they move down the gradient, diffusion or osmosis is usually involved and energy from the cell is not required.

Final Answer:
The processes that require no energy expenditure by the cell are Both osmosis and diffusion.